This invention relates to a seal system for the bearing chamber of a turbomachine. Particularly preferred embodiments related to a seal system for a gas turbine engine, featuring a single-stage compressor or a multi-stage compressor with relatively great differences in the pressure ratios of the individual stages, whereby the compressors are designed as axial and/or radial compressors and sealing of the bearing chamber against the turbomachine shaft or another rotating component fixed to that shaft is provided by contact-free seals, e.g., labyrinth seals, by means of sealing air, sealing steam or sealing gas.
Exemplary prior art refrences are U.S. Pat. No. 3,537,713, which includes so-called "labyrinth Seals" and U.S. Pat. No. 2,640,319, which shows bearings for a turbomachine shaft of conventional construction in FIGS. 1 and 1B thereof, which bearings are of the type contemplated in conjunction with the present invention.
More particularly, this invention relates to the conceptual design of contact-free seals operating with sealing air or sealing steam or sealing gas (labyrinth seals), in cases where only confined space is available for installation and/or in single-stage turbomachines.
Sealing systems of this type are commonly designed so that air or steam or gas is introduced into the bearing chamber via a restrictor body designed in the form of a labyrinth, thereby avoiding the leakage of oil. In such systems, the sealing medium (air or steam or gas) which unavoidably enters the oil compartment automatically causes heat to be transported into it because of the temperature and material characteristics of the sealing medium itself. Such heat may result in thermal stressing of the bearing and associated corresponding heating-up of the lubricating oil. Furthermore, the sealing medium entering the bearing chamber may lead to foaming of the lubricating oil and to all the consequent familiar problems associated with this phenomena.
Finally, the problems connected with heat dissipation from the bearing chamber and the recooling of the lubricating oil cannot be neglected.
In some configurations of thermal turbomachines, it is required that a bearing chamber has to be sealed against the highest pressure encountered in the entire machine system.
In the case of a multi-stage machine, where there are no space restrictions in designing the sealing for bearing chambers, the problems confronted are not so serious. In this case, however, it is necessary to provide sealing medium from a middle stage of the machine with a temperature and pressure which are both lower than the highest temperature and the highest pressure in the machine system. The leakage flow led off through a vent line is either carried overboard or, as the case may be, re-fed to the machine cycle at a suitable point.
In the case of a single-stage machine (e.g., radial compressor), however, no sealing air can be provided, the temperature and pressure of which are lower at the tapping point than at the machine end. Bearing sealing can therefore only be accomplished by means of a single labyrinth.
The same usually applies to multi-stage machines with great differences in the pressure head of the individual stages (e.g., axial-radial-compressors).
Bearing sealing has also to be accomplished by means of a single labyrinth in cases where, for instance, insufficient space can be provided for the use of a triple labyrinth.
This means, however, that in the examples mentioned air (or gas or steam) at the highest pressure and at the highest temperature encountered in the system has to be used as the sealing medium, this resulting in all the known adverse consequences for the bearing and the lubricating system (heating-up of the oil compartment, oil foaming, oil defoaming, oil-air separation, oil cooling, bearing temperatures, overall temperature level in the lubricating system, oil quantities).
As the pressure ratio across the labyrinth is automatically high, correspondingly great quantities of sealing medium enter the oil compartment.
An object of this invention is to solve the above-noted problems and to devise a contact-free seal system which, under the above-mentioned conditions, guarantees satisfactory sealing, especially in cases where only confined space is available for installation, with minimum thermal stressing of the bearings and the lubricating system.
According to one aspect of the present invention it is proposed to design the bearing chamber sealing system as a dual labyrinth system.
The pressure upstream of the first labyrinth, normally the highest pressure in the entire system, is reduced by this first labyrinth. After passing the first labyrinth, most of the sealing air (or steam or gas) is bled from the bearing area and re-fed to the machine cycle at a suitable point; the pressure of the remaining smaller portion of sealing medium is further reduced in a second labyrinth, this portion then entering the bearing chamber and sealing it thereby.
By means of a vent line extending into the area between the first and second labyrinth, the pressure obtaining at this point can be adjusted so that it is only slightly higher than the pressure in the oil compartment of the bearing. The pressure ratio is therefore low across the second labyrinth and consequently the sealing air (gas or steam) flow into the oil compartment is correspondingly small.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.